Refining dietary calcium and available phosphorus in laying hens: Effects on performance, egg quality, bone traits, and nutrient digestibility

This study evaluated the effects of graded dietary calcium (Ca) and available phosphorus (AvP) regimens on production performance, egg quality, skeletal integrity, and mineral utilization efficiency in Hy-Line Brown^® laying hens from 16 to 70 weeks of age, to estimate phase-specific optimal Ca and AvP levels. Experimental diets were formulated in two feeding phases (Phase 1: weeks 16-48; Phase 2: weeks 50-70). Within each phase, five Ca-AvP regimens representing approximately −20%, −10%, standard, +10%, and +20% deviations from the phase-specific recommendations were prepared and designated as CaP80, CaP90, CaP100, CaP110, and CaP120, respectively. A total of 180 pullets were allocated to treatments in a completely randomized design with six replicates per treatment and six hens per replicate. Results revealed that growth performance and egg production were unaffected by dietary Ca and AvP regimens throughout the experimental period. At 70 weeks of age, eggshell quality traits, including shell thickness and shell strength, were highest (p < 0.05) in hens fed CaP120; however, values in CaP90 and CaP100 were comparable. Tibial breaking strength and tibial mineral concentrations (Ca and P) showed similar responses, with no differences among CaP90, CaP100, CaP110, and CaP120 treatments. In contrast, ileal digestibility of crude ash, Ca, and P was improved (p < 0.05) in hens fed CaP80 and CaP90 diets. Regression analyses further refined dietary mineral recommendations. Linear-plateau and quadratic-plateau models indicated that higher Ca-AvP regimens were required to maximize skeletal mineralization and eggshell quality, with phase-specific optima ranging from 3.53-3.58% Ca and 0.30% AvP in Phase 1 (week 48) and 3.64-4.05% Ca and 0.29-0.32% AvP in Phase 2 (week 70). In contrast, quadratic regression analyses of ileal nutrient digestibility showed maximal absorption of crude ash, Ca, and P at lower dietary concentrations, typically 3.05-3.20% Ca and 0.26-0.27% AvP in Phase 1 and 3.09-3.53% Ca and 0.25-0.28% AvP in Phase 2. These findings support precision, phase-specific mineral feeding strategies that maintain performance and skeletal health while improving mineral utilization efficiency and reducing P oversupply in commercial layer production.